The field of the present invention is rotor members for high-speed turbomachinery. More particularly, the present invention relates to a high-speed centrifugal compressor rotor member for a combustion turbine engine.
Those skilled in the arts of design and manufacture of modern high performance aerospace turbine engines know that with any annular rotor member or disc rotating at high speed in the plane of the disc, the higher stresses are encountered at the surface of the central opening or bore. These bore stresses are developed because of the tremendous centrifugal force effective upon the material of the rotor member. Consequently, cracking or rupturing of the rotor member usually will begin at the bore surface. Propagation of such a crack through the material of the rotor member may result in eventual violent fragmentation of the rotor member in operation. Accordingly, a recognized design objective in high performance turbomachinery is to reduce to a minimum the mass of material manifesting centrifugal forces as stresses at the bore of the rotor member.
Yet another problem encountered in the turbomachinery art is that of high temperatures imposed upon rotor members. Usually the highest temperatures occur at the radially outer portions of a rotor member with progressively lower temperatures prevailing radially inwardly toward the bore thereof. Unfortunately, materials which have the comparatively high tensile strength necessary to prevent crack formation at the rotor member bore fail to have the high temperature creep resistance needed for the radially outer portions of the rotor member. To solve this problem, a variety of dual-alloy rotor members have been proposed wherein comparatively high tensile strength material is used at the rotor member bore and material having comparatively higher creep rupture strength is employed at the radially outer portion of the rotor member. Techniques of Hot Isostatic Pressing (HIP) have been used to bond the two or more sections of such a dual-alloy rotor member into a unitary or monolithic whole.
Particularly in the design, manufacture, and use of high performance centrifugal compressors the above-outlined difficulties, and others, combine to frustrate the application of conventional teachings for dual-alloy rotor members. For example, a high performance centrifugal compressor rotor for a combustion turbine engine, such as an advanced aircraft propulsion engine, may have a radially inner inducer portion whereat comparatively lower pressure air is received which exposes the material of the rotor member to only several hundred degrees temperature. On the other hand, the back plate of the centrifugal compressor rotor, which is axially opposite the inducer portion, may have a radially outer portion whereat temperatures of 1000 degrees Fahrenheit, or more, are encountered. All centrifugal compressor rotors rotate within a compressor housing providing, in the interest of aerodynamic efficiency, only a desirably small running clearance between aerodynamic blade members or portions of the rotor member and inner surfaces of the housing. Unfortunately, high temperature creep of the back plate portion of such a rotor member results in sections of the blade members moving axially toward the inducer side of the compressor rotor, as well as radially outwardly. Such plastic deformation of a centrifugal compressor rotor is sometimes referred to as "flowering". Flowering of a rotor eventually results in the running clearance being reduced until running contact and damage to the rotor member and housing results.